These studies have continued to focus on the mechanism by which plasma lipoproteins deliver lipids to cultured cells. Using high density lipoproteins obtained from humans with abetalipoproteinemia, we have shown that apolipoprotein B is not necessary for the binding of human lipoproteins to cells in culture. Heparin precipitation has also been found to correlate with the extent of lipoprotein binding in that the lipoproteins which are precipitated most readily by heparin are also bound and internalized most avidly to cells in culture. BIBLIOGRAPHIC REFERENCES: Mahley, R.W., and T.L. Innerarity. Interaction of canine and swine lipoproteins with the low density lipoprotein receptor of fibroblasts as correlated with heparin/manganese precipitability. J. Biol. Chem. 252:3980, 1977. Brown, B.G., R.W. Mahley, and G. Assmann. Swine aortic smooth muscle in tissue culture. Some effects of purified swine lipoproteins on cell growth and morphology. Circ. Res. 39:415, 1976.